Media captionTheresa May reveals the advice President Trump gave her over Brexit

Donald Trump told Theresa May she should sue the EU rather than negotiate over Brexit, she has told the BBC.

The US president said on Friday at a joint press conference he had given her a suggestion – but she had found it too “brutal”.

Asked by the BBC’s Andrew Marr what it was he had said, she replied: “He told me I should sue the EU – not go into negotiations.”

She defended her blueprint for Brexit and urged her critics to back it.

She said it would allow the UK to strike trade deals with other nations, end free movement of people, and end the jurisdiction of the European Court of Justice.

A White Paper published on Thursday fleshed out details of her plan, which advocates close links with the EU on trade in goods, but not services.

‘Remained a Remainer’

Before the paper was published, Brexit Secretary David Davis and Foreign Secretary Boris Johnson resigned, saying it would not deliver the Brexit people voted for in the 2016 referendum.

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Media captionPrime Minister Theresa May and US President Donald Trump hold a joint press conference at Chequers

Mrs May laughed off the president’s legal action suggestion, saying she would carry on with negotiations, but added: “Interestingly, what the president also said at that press conference was ‘don’t walk away’.

“Don’t walk away from those negotiations because then you’ll be stuck. So I want us to be able to sit down to negotiate the best deal for Britain.”

But hours later he said a US-UK trade deal would “absolutely be possible”.

Leading Tory Brexiteer Jacob Rees-Mogg has called the White Paper a “bad deal for Britain”. He says it would lead to the UK having to follow EU rules with no say in how they are made.

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Media captionJacob Rees-Mogg tells the BBC the prime minister’s Brexit plan goes against promises she made

He told the BBC’s Sunday Politics: “The government unfortunately believes that Brexit is not a good thing in itself, it seems to think it has to be tempered by non-Brexit.”

He said Mrs May, who campaigned to keep Britain in the EU in the 2016 referendum, had failed to grasp the “enormously positive” opportunities offered.

He described her as a “Remainer who has remained a Remainer”.

He also said she would have to change her policy in order to get it through Parliament, without having to rely on Labour votes.

Mrs May urged Brexiteers in her own party to “keep their eye on the prize” of Brexit – and said her plan was the only workable way to deliver it.

‘Very difficult to bring an action’

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Analysis by BBC legal correspondent Clive Coleman

Frankly, it is difficult to see any grounds for the UK suing the EU.

Like any other member state, the UK can sue the EU in relation to any specific measure it has taken which breaches EU law.

Such action would be heard at the European Court of Justice, the ultimate arbiter of EU law.

An example would be if the UK was denied agricultural subsidies, or structural funds to which it was entitled under EU law.

The Conservative government of David Cameron successfully sued when the European Central Bank said it would only license financial institutions within the Eurozone as clearing houses for transactions in euros.

The UK and the EU have not reached a Brexit agreement yet, so there can be no action for breach of that agreement.

Parties to a negotiation are under what are known as “procedural duties” – for instance, to act in good faith.

But it is very difficult to bring an action, within a negotiation, on that basis. Some would say that even attempting to do so would seriously harm the negotiation.

Mrs May’s message comes ahead of crucial Commons votes on trade and customs policy in the coming week, with Tory Brexiteers tabling a series of amendments to the legislation.

“Some people are saying they want to vote in the Trade Bill to keep us in the customs union. I say that’s not acceptable,” Mrs May told Andrew Marr.

“That’s not what the British people voted for.

“Others are saying that perhaps we cannot have the bill at all. That would be damaging to our ‘no deal’ preparations.

“So let’s just keep our eyes on the prize here. The prize is delivering leaving the European Union in a way that’s in our national interest.”

Mrs May insists her plans would allow the UK to strike its own trade deals, despite agreeing a “common rulebook” with the EU on cross-border trade.

She said such rules were needed to protect jobs in firms with supply chains that crossed borders and deal with the Irish border issue.

Labour Party chairman Ian Lavery said Mrs May’s “so-called plan” did not “stand up to scrutiny”.

“No-one – not the public, Parliament or the Conservative party – is happy with Theresa May’s offer. This has descended into a shambles,” he said.

Labour MP Ian Murray, a member of the People’s Vote campaign, said the British people needed a vote on the final deal.

Labour Deputy Leader Tom Watson said it was not the party’s policy to back another referendum – but said it should not be ruled out.